How Long Will a Generator Run on a Tank? (Load vs Fuel Math)
Calculate fuel burn rates per hour depending on total operational electrical load.
The Rule of Fuel Consumption
A generator does not burn fuel at a constant rate. Just like a car driving uphill burns more gas than a car coasting downhill, a generator heavily loaded with appliances will burn fuel much faster than one powering a few light bulbs.
Manufacturers typically advertise runtime at either a 25% load or a 50% load.
Estimating Gasoline Consumption
As a rough engineering baseline, a standard gasoline generator will consume about 0.14 to 0.16 gallons per hour (GPH) for every 1,000 watts of load.
Example: Running a 4,000 Watt Load
4,000W / 1,000 = 4.
4 × 0.15 = 0.6 Gallons Per Hour.
If your generator has a 6-gallon tank, it will run for 10 hours at this load (6 / 0.6 = 10).
Propane (LPG) vs Gasoline
Many modern generators are "dual-fuel." While propane is incredibly convenient and never goes bad, it contains about 25% less energy per gallon than gasoline.
- Gasoline: ~114,000 BTU per gallon
- Propane: ~91,500 BTU per gallon
Because of this, if you switch your generator from gasoline to propane, it will burn through fuel faster for the exact same electrical load, and its maximum wattage output will drop by about 10%.
Inverter vs Conventional Generator Fuel Economy
Conventional open-frame generators must always run at a constant 3600 RPM to produce 60Hz electricity, regardless of whether you are pulling 100 watts or 5000 watts. This wastes a lot of fuel at low loads.
Inverter generators, however, have microprocessors that electronically synthesize the 60Hz wave. This allows the engine to throttle down to a very slow idle when the electrical demand is low, drastically improving fuel economy.
| Generator Type (3500W) | Load | Runtime on 3 Gallons |
|---|---|---|
| Conventional | 500W (Light Load) | 10 hours |
| Inverter | 500W (Light Load) | 18 hours |
| Conventional | 3000W (Heavy Load) | 6 hours |
| Inverter | 3000W (Heavy Load) | 6 hours |